Cell structure, device and method for gas analysis

ABSTRACT

The invention relates to a gas analysis based on the mobility of ions. The invention relates to a cell structure of an analysis device, the cell structure comprising the reference cell ( 201 ), the ionisation section ( 202 ) and the analysis cell ( 203 ) for identifying the electric mobility of ions. The invention also relates to a method for identifying the ions. Further, the invention relates to a system for identifying the ions.

RELATED APPLICATION

This application is a division of application Ser. No. 10/509,198 filedJun. 29, 2005, which claims priority to Application No.PCT/FI2003/200226 filed Mar. 25, 2003, which claims priority toApplication. No. FI 20020565 filed Mar. 25, 2002, each of which ishereby fully incorporated herein by reference.

OBJECT OF THE INVENTION

The invention relates to analysis technique used in spectrometry basedon the mobility of ions. The invention especially relates to a cellstructure used in the analysis technique of gas, as disclosed in thepreamble of the independent claim concerning it.

The invention also relates to a device for identifying the substances inflowing gas, as disclosed in the preamble of the independent claimconcerning it. The invention also relates to a system for identifyingthe substances in sample gas, as disclosed in the preamble of theindependent claim concerning the system. Further, the invention relatesto a method for identifying the substances in flowing sample gas, asdisclosed in the preamble of the independent claim concerning it. Theinvention also relates to a method for measuring the sample gasvelocity, as disclosed in the preamble of the independent claimconcerning it.

DESCRIPTION OF THE TECHNICAL BACKGROUND

Of the structural units of gas, atoms and/or molecules formed by them aswell as ions may be mentioned. A single ion or some other structuralunit in the gas can momentarily move with a deviating speed and/or to adirection deviating from the flowing direction and/or speed of the gasitself, but on average, a single ion or some other structural unit ofthe gas in it, however, moves along with the gas. Also short-livedradicals can occur in the gas. Some molecules of the gas can also formloose clusters with polar molecules so that the bond between them issmaller, compared to the strength of a chemical linkage.

A gas sample is a sample to be taken from gas, estimated to representthe gas, from which the sample is taken, with a certain accuracy. Asample gas is a gas, the composition of the gaseous components of whichrepresents the gas sample. The gas sample can also be an aerosol, inwhich case, in addition to the gaseous phase of the actual sample gas,there may also be present particulate bodies, in a macroscopic sensesmall pieces, particles, comprising other phases.

Identifying a gas on the basis of certain properties of its structuralunits can be performed with electrical methods provided that there is asufficient amount of the structural units of the gas in the ionisedstate. At least two techniques are known for identifying ions fromflowing gas with electrical methods, the IMS technique and the Drifttube, of which also the name drift technique is used. In the IMStechnique, ions are analysed from a gas flow, which travels between suchmeasuring electrodes that form an open aspiration condenser. Theaspiration condenser has an electric field, the direction of which isperpendicular to the direction of the flow. The electric field deviatesions from the gas flow onto a plate of the aspiration condenser. Theflight time and/or flight range of the ions is measured so that it ispossible to separate the mobility of ions.

In the Drift technique, ions move in the electric field from acollection lattice to a measuring electrode, from which the magnitude ofelectric current is measured as a function of time. The zero point foreach measurement is set to the zero point of the lattice pulse to begiven to the collection lattice, and the ions to be measured move to themeasuring electrode usually through a carrier gas with suitableproperties. Due to its principle, separate circulations are generallyneeded for the sample and the carrier gas in the practical realisationof the Drift technique so that the cell is inevitably of a closedstructure, as is also the case with the gas circulation.

An IMS technique is known, in which an open cell according to thesimplified schematic diagram shown in FIG. 1 is used in the measurementof the sample gas mobility. The cell has an input at the first end ofthe analysis chamber 106, the gas sample flow 100 going to which isillustrated by an arrow. The chamber 106 itself is restricted by theplates 102 and 108. The cell has an electrode pair consisting of theelectrodes 103 and 104 for detecting the ions 101 in the gas sample flow100. The electrode 103 is attached to the plate 102 and the electrode104 to the plate 108. The electrode 103 has a certain potential and theelectrode 104 a certain second potential. The potential of the electrode104 is generally close to the ground potential for placing the electricfield 105 between the electrodes 103 and 104 and, on the other hand, forgenerating the voltage signal to be generated against the groundpotential. The cell shown in FIG. 1 operates so that, as the gas ion 101arrives at the space between the electrodes along with the gas sampleflow 100, the electric field 105 interacts with the ion 101, in whichcase the interaction force causes a change of the travelling directionof the ion 101 and, in a certain case, its aggregation to the plate 104so that the change of charge caused there by the aggregating ions isdetectable as an electric current and changeable, for example, to avoltage signal. In cell solutions according to FIG. 1 for identifyinggas on the basis of the mobility spectrum of its ions, an alternatingvoltage of nominally constant value can be used for providing theelectric field 105 changing along with it. In this case, the strength ofthe electric field 105 can be varied, for example, sinusoidally, and/orseveral such electrode pairs as the pair formed by the electrodes 103and 104 is used for analysing the charged particles so that the pairsare also attached to the cell limited by the plates 102 and 108 andmounted sequentially, following one another in the direction of flow sothat there is an angle, generally a right angle between a mean velocityvector of the sample gas flow 100 and the directional vector of theelectric field 105. For example, ions with certain mobility can then bepicked up to the plate 104, and slightly different ions can be picked upto a similar second plate for forming the mobility spectrum, and thesample gas can be identified with the help of it.

Cell geometries are also known, in which an electric current caused byions is detected by electrodes at opposite ends of the chamber so thatthe angle between the gas flow and the average direction of travel ofthe ions is approximately 180.degree. The gas in the drift chamber ofthe cell can, be let to drift through the drift chamber, for example,with the help of the flow; in some solutions however, also to theopposite direction from the average movement of the ions under theforces created by the electric field.

In the known technique, the incoming sample is charged substantiallyimmediately, and the ions are let to drift along with the flow passingthrough the chamber but, on the other hand, according to the directiondetermined by the electric field; in some cases, also deviating from thedirection, nevertheless, towards the current target or a respectiveelectrode 104 for collecting the ions, which can also be located, forexample, at the opposite end of the analysis chamber from the sampleinput arranged for sampling. When hitting such a current target as theelectrode 104, the ion causes a change of the electric charge in it,which is interpreted as a current signal and processed into a suitableform with signal processing means.

Charging the gas sample can be performed in many different ways.Radioactive sources, light and corona discharge may be the best knowncharging techniques as such so that the facts generally known aboutcharging depend on the charging mechanism desired to be used and/or onthe purpose of use of the charged material, as has been explained inpublications dealing with the known technology.

However, the known state-of-the-art cell structure has drawbacks. One ofthese is connected to the structure of the condenser formed by theelectrodes. In the condenser, the change of potential on the plate 103can be seen in the measurement made from the plate 104. In addition,variations in air humidity and temperature have a detrimental influenceon the properties of the condenser, which makes the processing of thecurrent signals caused by the ions more difficult and thus causesuncertainty in the forming of the mobility spectrum, which makes theidentification more difficult.

Known IMS technique is described in a patent publication U.S. Pat. No.5,455,417, the device according to which is illustrated by thecross-sectional drawing in FIG. 1B: The gas entering from the input 128is heated in constant temperature with the help of the aluminium part119, which contains the heater 127 controlling its temperature. The gasis charged with the help of the radioactive source 129, after which thegas advances to the analysis cell 125 having the plate electrode 121 andfront electrode 122 and collection electrode 123 for the stepwiseadjustment of a certain voltage and thus an electric field between theelectrodes 121, 122 and 123, as is explained in the patent publication.By using the electric field in the way mentioned, it has been attemptedto make the conventional aspiration condenser in FIG. 1B work in a moreperfect manner. Among others, the temperature sensor used in theadjustment of temperature, the gas output 120 and the circuit boards 124and 126 have been drawn to FIG. 1B, electronic components having beendrawn to the surface of the latter circuit board 126.

The patent publication also discloses a method related to the technique,in which a sample including the substance to be analysed, the analyte,is first collected and charged. However, the patent specificationmentions that, in this case, the concentration of the analyte has to besufficiently high in the sample in order to achieve a saturation stagein the charging. The mobility of ions is determined from the charged gassample. The concentration of the analyte in the sample is determined onthe basis of the mobility.

The technique has its drawbacks. The massive aerosol particles advancingto the analysis cell 125 after the accumulator can get through the fieldformed by the electrodes 121 and 122, and most disadvantageously, causeconsiderable signal distortion on the analysis electrode 123, especiallyif and when they can carry a considerable electric charge. Further, thepossible presence of aerosol particles in the accumulator can have adetrimental effect on the later stages, such as the mechanical and/orelectrical blocking of the next analysis chamber, in which case theoperation is made more difficult, and the reliability of the analysisresult suffers. The possible re-suspension and/or related contactcharging can also detrimentally transfer the charge to a wrong place.Another matter is related with heating. Namely, when transferring fromheated sections to colder sections, the changes in temperature can causephase transitions from gas phase to liquid phase and/or solid phase. Inthis case, the phenomenon in question is the forming of particles,nucleation, which has several subtypes, depending on the starting pointsof the particle formation. Especially the ion-induced nucleationtriggered by radiation and, for example, the heterogenic nucleationtaking place in structural defects on surfaces can in some circumstancescause the formation of particle-shaped material and its aggregation toplaces detrimental for the identification of ion mobility.

State-of-the-art solutions are further limited by a certain slowness inthe changes of voltage so that it is also possible that changesoccurring in the sample gas during a single measurement can influencethe final result.

SHORT DESCRIPTION OF THE INVENTION

The object of the invention is to avoid the drawbacks according to thestate of the art. Further, the object of the invention is to eliminatethe drawbacks the variations in air humidity and temperature cause tothe identification of ions. In addition, the object of the invention isto achieve a system, which makes possible the efficient reporting ofmeasurement results. The object of the invention is further to provide agas measuring device with the structure according to the invention. Inaddition, it is the object of the invention to provide a method forusing the structure according to the invention in the mobility analysisof ions.

The objects of the invention are achieved with such a structure of a gasmeasuring device, which has a cell structure comprising a referencesection, an ionisation section and an analysis section in said order, asarranged in the direction of flow of the gas to be measured.

The cell structure according to the invention is characterised in that,which is disclosed in the characterising part of the independent claimconcerning the cell structure according to the invention.

The gas measuring device according to the invention is characterised inthat, which is disclosed in the characterising part of the independentclaim concerning the gas measuring device according to the invention.

The method according to the invention for identifying substances inflowing gas, based on the electric mobility of ions, is characterised inthat, which is disclosed in the characterising part of the independentclaim concerning the method according to the invention, for identifyingsubstances in flowing gas, based on the electric mobility of ions.

The system according to the invention for identifying substances in ionform from flowing gas on the basis of their electric mobility ischaracterised in that, which is disclosed in characterising part of theindependent claim concerning the system.

The method according to the invention, for electrically determining theflow rate in an aspiration condenser, is characterised in that which isdisclosed in the characterising part of the independent claim concerningthe method according to the invention for electrically determining theflow rate in an aspiration condenser.

The dependent claims depict other advantageous embodiments according tothe invention.

The cell structure according to the invention is arranged foridentifying a substance in a carrier gas, based on the analysis on thegaseous state of the mobility spectrum characteristic to the substance.For producing the mobility spectrum, a sample, a gas sample, is takenfrom the carrier gas, led to the cell structure of the device accordingto the invention; a reference signal is generated on the basis of thesample; the gas sample is ionised; the ionised sample gas is analysed;an analysis signal is generated in the analysis, and the mobilityspectrum of the ions is determined from the sample gas on the basis ofthe reference signal and the analysis signal.

The cell structure of the device according to the invention is open in acertain way, and it comprises a drifting chamber between the input forthe gas sample and the output for the analysed sample gas, the driftingchamber containing a reference section, an ionisation section and ananalysis section in said order in the direction of travel of the sample.

The reference section is arranged to the cell structure according to theinvention for generating the reference signal. The reference section hasthe reference cell and in it an electrode pair, a reference electrodepair having a certain reference electrode for generating the referencesignal on the basis of the charges of ions arriving to the referenceelectrode. In this case, the reference signal is intended to be formedfor eliminating the factors depending on the environmental factors of anunionised sample and such capacitive phenomena from the final mobilityspectrum of ions and thus from the analysis result that can have acertain detrimental influence on the analysis signal itself and thus onthe result.

The ionisation section has an ionisator, a charger, for producing ionsand for bringing them into contact with the gas parts intended to becharged. The still unionised sample, intended to be entered into theionisation section, is charged in a certain way for forming ions intothe sample.

The analysis section has an analysis cell and in it a pair ofelectrodes, a pair of analysis electrodes, containing an analysiselectrode, which is arranged so that ions can be collected onto it withthe help of an electric field, so that the changes in charge, formingonto an analysis electrode in a way determined by the mobilities of theions, can be interpreted as a certain electric current signal. On thebasis of said electric current signal and, on the other hand, also withthe help of the reference signal, an ion mobility distribution in thesample can be formed so that the substance in the sample can beidentified on the basis of its ion mobility distribution. The use of thereference electrode in the formation of the mobility distribution isadvantageous in the elimination of the influence of environmentalfactors so that identifying the substance from the gas is reliable. Inaddition, by using the reference electrode pair, drawbacks caused by thecondenser structure to the accuracy of the mobility spectrum can beeliminated.

The analysis device according to the invention has the cell structureaccording to the invention. The analysis device according to theinvention also most preferably includes filter means for removingparticulate material from the gas sample; in other words, for purifyingthe gas as to a sample gas. The filter means can, for example, comprisea HEPA-type filter, a membrane or fibre filter, an electric filter, animpactor, or some other filter for collecting particles, or acombination of these, arranged especially for removing heavy aerosolparticles from the gas sample, which particles can carry several chargeswith them or otherwise have a detrimental influence on the analysisresult.

The analysis device according to the invention can also comprise controlmeans, for example, for controlling the operation of the ionisator. Theanalysis device according to the invention can have means forcontrolling the supply of the operating voltage of the referenceelectrode pair and/or analysis electrode pair. The analysis deviceaccording to the invention can also comprise certain first signalprocessing means for processing the signal intended to be transmittedfrom the reference electrode.

The analysis device according to the invention can also comprise secondsignal processing means for processing the signal intended to betransmitted from the analysis electrode. The first and second signalprocessing means can be functionally connected to comparison means, inconnection of which also memory means can be provided.

In connection of the comparison means, there most preferably is amicroprocessor for controlling the comparison means. The microprocessorcan be physically separate from the comparison means. There can also beseveral microprocessors to be used in different tasks for achievingcertain independence. A microprocessor can also be arranged so that itcan be used for forming a control signal to the ionisator, to the meansfor forming the reference voltage and/or the means for forming theanalysis voltage, for example, through specific control means eitherindirectly or directly by controlling said means and/or ionisator.

In a system according to an advantageous embodiment of the inventionthere is an analysis device having functional control means forcontrolling the analysis operation of the device by remote control,preferably wirelessly, for example, on the basis of data transmissionoccurring with the help of electromagnetic radiation, but possibly alsothrough an electric and/or optical cable. In this case, the mentionedanalysis device according to an embodiment of the invention, a remotedevice, most preferably contains transmitter means and receiver means,for example, combined as transmitter-receiver means, arranged forreceiving the control signal controlling the operation of the analysisdevice and/or for transmitting the data describing the measurementresults and the status of the remote device to a second devicecommunicating with the remote device.

So it is possible, for example, to control the cell structure of thedevice according to the invention from the outside of the devicewirelessly and/or with the help of a cable, the cell structure beingplaced, for example, to a fume hood or a similar place isolated from theenvironment in a certain way. When applicable, the control can berealised wirelessly and partly by cable.

SHORT ACCOUNT OF THE FIGURES

FIGS. 1A and 1B illustrate the known technique as follows:

FIG. 1A illustrates a cell according to the known technique; and

FIG. 1B illustrates another cell according to the known technique.

The invention is next explained in more detail, referring to theadvantageous embodiments shown as examples and to the enclosed drawings2-5, in which

FIG. 2 illustrates as a diagram the cell structure of an advantageousembodiment according to the invention;

FIG. 3A illustrates a diagram for a first order cell structure accordingto an advantageous embodiment of the invention;

FIG. 3B illustrates a diagram for a second order cell structureaccording to an advantageous embodiment of the invention;

FIG. 4A illustrates a diagram for a gas measuring device according to anadvantageous embodiment of the invention;

FIG. 4B illustrates a diagram for another gas measuring device accordingto a second advantageous embodiment according to the invention; and

FIG. 5 illustrates a method according to the invention for identifyingsubstances in flowing gas.

Same reference numbers and markings are used of corresponding parts inthe Figures.

DETAILED DESCRIPTION OF ADVANTAGEOUS EMBODIMENTS ACCORDING TO THEINVENTION A. First Advantageous Embodiment

FIG. 2 shows on a very coarse level an exemplary diagram of the cellstructure 200A according to an advantageous embodiment of the invention.The cell structure 200A has a drifting chamber 200 for sample gas, onestructural unit 210 of which has been drawn into the figure. The cellstructure 200A, its drifting chamber 200, has the reference section 201,the ionisation section 202, and the analysis section 203. Forillustrative purposes, the reference section 201 is separated from theionisation section 202 by the vertical broken line 220. For illustrativepurposes, the ionisation section 201 is separated from the analysissection 203 by the vertical broken line 221. The input 204 of the cellstructure 200A for the gas sample flow 100 and the output 205 for theanalysed sample gas are functionally located at different ends of thecell structure 200A so that the reference section 201, the ionisationsection 202 and the analysis section 203 of the cell structure arelocated in said order in the direction of travel of the sample,irrespective of the possible bendings of the drifting chamber 200. Onthe basis of the diagram drawn in FIG. 2, the cell structure 200A hasthe substantially straight drifting chamber 200, but on the basis ofwhat is shown in the invention, it is obvious for one skilled in the artthat the sections of the drifting chamber 200 can also be arranged tobend, for example, for saving space, in which case the ends of the cellstructure 200A can be located physically very close to each other.

It is stated that the cell structure according to an advantageousembodiment of the invention can be an open cell structure of firstorder, substantially according to the example in FIG. 3A. The cellstructure according to another advantageous embodiment of the inventioncan be a cell structure of second order, substantially according to theexample in FIG. 3B. FIG. 3A illustrates, more than FIG. 2 in detail, theinternal structure of the cell structure according to an advantageousembodiment of the invention. The cell structure in FIG. 3A is an exampleof a first order cell structure. In FIG. 3A, for the illustrativepurposes, also the vertical broken line 220 separating the referencesection 201 from the ionisation section 202 and the vertical broken line221 separating the ionisation section 202 from the analysis section aremarked in the drifting chamber 200 of the cell structure 200A. Let it bestated that the separation indicated by the broken lines 220 and 221 isnot desired to restrict the invention. If the ionisation section 202 hasa radiation source, it may be preferable to separate it 202 from thereference section 201 and/or analysis section 203. In such case, theremay also be physical equivalents present for the broken lines 220 and/or221 in the drifting chamber 200 to prevent the ionising radiationoriginating to the ionisation section from influencing the sectionsseparated from the ionisation section. In such a case, the separatingwall corresponding to the broken line 220 can also have a bendinggeometry for allowing the travel of gas, on the one hand, and forsimultaneously preventing the travel of radiation to other sections ofthe drifting chamber 200, on the other hand. Also the separating wallcorresponding to the broken line 221 can have a bending or partlyapertured geometry for allowing the travel of gas, on the one hand, andfor simultaneously preventing the travel of radiation to other sectionsof the drifting chamber 200, on the other hand.

In FIG. 3A, the drifting chamber 200 has a section corresponding to thereference section 201, the reference cell, which is substantiallylocated at the place of the reference electrode pair structureconsisting of the reference electrodes 303 and 304. For separatingcertain electrodes in FIG. 3A from the plates 302, the electrodesupports 309 and 311 of insulating material have been drawn to theFigure. They can also be integrated as part of the structure of theplate 302. The electrode 303 is intended to be connected, for example,via the voltage source 405 shown in FIG. 4A for arranging the electricfield 305 between the electrodes 303 and 304. The voltage source is notshown in FIG. 3A. The electrode 304 is then substantially in constantpotential close to the ground potential. As ions arrive at the electrode304, the potential of the electrode 304 changes. The charge arrivingwith each arriving ion slightly changes the potential of the electrode304 so that the changes of the electrode potential are relatively smallper charge of an arriving ion. As ions arrive at the electrode 304, thechanges of its charge can be detected as electric current. Mostpreferably the detection of changes of charge can be made with anelectrometer or similar or, for example, with a suitable current-voltageconverter. In this case, for detecting the changes of charge, theelectrode 304 can be used as the sensor for the electrometer the changesof charge of which are detected. With the help of the current-voltageconverter, an output signal of the electrometer can then be formed, andon the basis of it a reference signal, either directly or by processing,for example, a voltage signal in relative to the ground potential.

In an analysis situation, the electric field between the electrodes 303and 304 of the reference cell can then be time-dependent, in which casethe waveform describing the time dependency is most preferably sine,triangle or ramp, for providing a scanning electric field. In theinvention it is not wanted to restrict the waveform of said electricfield to any specific one, but the waveform can also be a so-called freewaveform so that it can be presented as a series of terms to be formedwith the help of an exponential functions. Also some other arrangements,known for one skilled in the art, can be used for detecting weak changesof charge and their converting into a current and/or voltage signal.Said kind of detection of a current and/or voltage signal based on thechanges of charge can also be arranged to some other reference potentialthan relative to the ground potential. It may also naturally be arrangedso that changes of charge are detected from the electrode 303 in apotential, which has a high absolute value in relation to ground, buttaking into account the voltage between the electrodes 304 and 303 uponforming the actual desired signal can then require special arrangements.In the invention, it is not wanted to restrict the direction of theelectric field 305 merely to the momentary case drawn to the Figure, butsome other, a static field can be used, but also such an alternatingfield which has a momentary direction, an amplitude, frequency and/orwaveform.

In FIG. 3A, the drifting chamber 200 also has the ionisation section 202as in FIG. 2. In the diagram illustrated by FIG. 3A, the ionisationsection is separated from the rest of the drifting chamber 200 by thebroken lines 220 and 221. The ionisation section 202 is substantiallyrestricted to the area limited by the electrodes 307 and 308. Electrodes307 and 308 have been drawn in FIG. 3A, between which, for example, acorona discharge can be provided, by a controllable voltage source 405(FIG. 4A), for example, so that it is possible to charge, produce ions301 into the gas travelling in the area there between the electrodes 307and 308 by an electric field. For producing the ions 301, also anionising field 306 can be used, which can be, for example, a radiationfield provided by radiation generation resulting from of radioactivity,a radiation field based on ultraviolet radiation, and/or an electricfield. An example illustrates the direction of the ionising field 306 byan arrow, for example as a direction of travelling radiation; but alsosuch an ionising field can be used which has components to severaldirections, or the direction can be some other direction than the oneshown by the arrow. When applicable, the electrodes 307 and/or 308 canthen be replaced by a material or piece that produces radiation, forexample, by a strip containing a radioactive substance. By using aradioactive charger and an electric field as a combination, it is alsopossible to restrict the access of so-called recoil atoms, resultingfrom radioactivity, to the sections located after the ionisation sectionin the cell structure and to thus improve the measuring itself.

FIG. 3A shows support 310 supporting the electrode 307. With thegeometry of the support 310 and of the electrode 307, it is possible toinfluence also the range of radiation into other parts of the driftingchamber. The support 310 can also be shaped so that it further compriseslimits for separating the ionisation section from the rest of thedrifting chamber 200, corresponding, for example, to the separationindicated by the broken lines 220 and 221, for restricting theionisation effect of the charger to a certain section of the driftingchamber. However, use of the support 310 is not necessary.

The radiation source can be located on the same level with some of theelectrodes 304, 314, 303 and 313 listed as an example. In the firstorder cell structure it is also possible to locate the radiation source308 to the other side of the plate 302 than in FIG. 3A, so that theradiation source can be structurally arranged to be, easily replaceable.In this case, the plate 302 itself and/or the separation radiationcontrol plate intended to be attached to it has a set of holes of whichat least one hole has a certain shape, at least one diameter and lengthas well as location in relation to the other holes for forming a certainpattern. The shape of the hole can then be angular, rectangle orcircular, for directing the radiation, originating from the radiationsource through said at least one hole to the ionisation section, inwhich the gas is travelling, for optimising the dose rate resulting tothe gas in a most appropriate manner for the charging of the gas. Withthe shape of the holes, especially their length and cross-sectionperpendicular to the longitudinal direction and also the shape, it ispossible to influence the distribution of radiation in the ionisationsection. The same principle can also be applied to a second order cellstructure so that the radiation source can be arranged to be modular andreplaceable, for example, by fast couplings for connecting the radiationsource and the radiation guiding plate to the charger section. In thiscase, it is possible to influence the directional pattern of radiationin a similar way as has been explained in connection of the first ordercell structure.

In FIG. 3A, the drifting chamber 200 has a section corresponding to theanalysis section 203, an analysis cell, which occurs co-locatedsubstantially at the analysis electrode pair consisting of the analysiselectrodes 313 and 314. The electrode 313 is intended to be connected tovoltage, for example, through the voltage source 413 (FIG. 4A) forarranging the electric field 315 between the electrodes 313 and 314. Thevoltage source is not shown in FIG. 3A. In this case, the electrode 314is substantially in constant potential close to the ground potential.The charge arriving with each arriving ion slightly changes thepotential of the electrode 314 so that the changes of potential of theelectrode 314 calculated per one arriving ion are relatively small. Asions arrive at the electrode 314, its changes of charge can be detectedas electric current. Most preferably, the detection of changes of chargeis made with an electrometer or similar or, for example, with a suitablecurrent-voltage converter. In this case, the electrode 314 can be usedfor detecting the changes of charge as the sensor for the electrometerthe changes of charge of which are detected. It is then possible to forman output signal of the electrometer with the help or thecurrent-voltage converter, and on the basis of it directly or bymodifying an analysis signal, for example, a voltage signal in relationto the ground potential. Also, some other arrangement, known for askilled man in the art, can be used for detecting weak changes of chargeand for converting into a current and/or voltage signal. The detectionof a current and/or voltage signal based on the said kind of changes ofcharge can also be arranged to some other reference potential thanrelative to the ground potential.

In an analysis situation, the electric field between the electrodes 313and 314 can then be time-dependent, in which case the waveformdescribing the time dependency is most preferably sine, triangle orramp, for providing a scanning electric field. It is not intended in theinvention to restrict, the waveform of the electric field to anyparticular form, but the waveform can also be a so-called free waveformsuch that can be presented as a series of terms derivable form anexponential function. It may naturally also be arranged so that changesof charge are detected from the electrode 313 in a potential with a highabsolute value relative to the ground, but when forming the actualdesired signal, in such a case taking into account the voltage betweenthe electrodes 313 and 314 can require special arrangements. In such acase, also some advantages achieved by the use of the reference cell maybe partly lost in the determination accuracy of the mobility. It is notintended in the invention to restrict, the direction of the electricfield 315 merely to the momentary case drawn in the Figure, but alsosome other, static electric field can be used, as well as alternatingelectric fields with a momentary direction, an amplitude, frequencyand/or waveform.

In embodiments according to the invention, in the first order cellstructure as well as in the second order cell structure, the dependencyof the collection efficiency of ions on the electrode voltage betweenthe cell electrodes is taken into account for the both, the analysiscell and the reference cell. Relating to the identification of ions, thedependency of the collection efficiency on the voltage between theelectrodes of the cell can also be taken into consideration within othercells, such as a front cell and/or back cell, also in a first order cellstructure with a front cell and/or back cell.

It is stated on the reference electrode and the analysis electrode that,by using one such electrode, a voltage signal can be formed as baseddirectly on the change of said electrode in potential relative to theground potential, but in such a case the possible influence of saidchange in potential on the collection efficiency of ions onto saidelectrode has to be considered.

As based on the gas velocity, it can be taken into account the moment oftime, at which the momentary value of the reference signal has beenformed with the help of the reference electrode. In such a case, apotential interference advancing with the gas into the analysis cell canbe eliminated in a right phase from the signal used for analysing theion mobility so improving the measurement accuracy.

The status of the gas flowing to the area of the reference electrodepair can be described by several physical quantities. In FIG. 3A, thephysical state of the sample gas in a gas sample is illustrated, as thegas arrives at the reference section of the cell structure, by a firststate vector Y.sub.sto.sub.—.sub.i=Y.sub.sto.sub.—.sub.i(T, RH, S.sub.i,.mu.sub.xi, r, . . . , N.sub.i), which has an finite number ofcomponents. A set of components of the state vector can then bedescribed as follows: T=temperature of the gas or similar, RH=relativehumidity, S.sub.i=the saturation ratio for the component i in the gas,mu.sub.xi=mass-absorption coefficient for the radiation type x with acomponent i in the gas, r=gas density, N.sub.i=molar fraction of thestructural units of a component i in the gas. Most preferably, thesequence formed by the components of said state vector is free, i.e. thecomponents of the state vector are not dependent on each other. Inpractice, for measuring technical reasons, it however may be necessaryto select also such components to the sequence that one has tocompromise with the freedom of the sequence. In addition to the onesmentioned, components of the first state vector can be the resistivityof a component i of the gas, viscosity, pressure, partial pressure, amean free path of a gas molecule of the gas component i in certainpressure and temperature and with a fraction of a certain gascomposition, diffusion coefficient and/or mechanical mobility of thetype i of a gas molecule, and the turbulence/laminarity of the flowfield. However, it is not intended in the invention to restrict into anycertain combination of said quantities.

The flow state of the sample gas in the analysis section has beenillustrated by a second state vector Y.sub.sto.sub.—.sub.o in FIG. 3A,which is the same as Y.sub.sto.sub.—.sub.i with a certain accuracy. Bypresuming that the first and second state vector are identical accordingto their reference components, the electric current detected on theanalysis electrode 314 can be corrected by a correction to be formed onthe basis of the electric current detected from the reference electrode304, which can be formed, for example, on the basis of the referencesignal. If the first and second state vectors are not identical with asufficient accuracy, the difference can be taken into consideration bycalibration.

Most preferably, the electric field 305 between the reference electrodepair has been arranged in the same way as the electric field between theanalysis electrode pair, both in relation to the amplitude, strength andfrequency and the phase, as is shown in the Figure. Nevertheless, it ispossible to deviate from this, if it is only known how the deviationwill influence the reference signal and thus the mobility spectrum ofthe ion under analysis so that the deviation can be taken intoconsideration in the identification of the substance in the sample. Inthis case it is also possible to take into account the possibleinfluences on the state vector Y.sub.sto.sub.—.sub.i as theidentification advances, also iteratively. It is also possible tocompensate, for example, structural uncertainties caused by themanufacturing accuracy of mechanics, by using such a voltage source, inwhich it is possible to separately adjust the phase and amplitude of thevoltage feeding the cell, most preferably independently from each other.Besides continuous adjustment, the adjustment can then also beunderstood to mean the setting of the limit for the adjustment area andthe non-recurring set-up occurring in connection of the setting of thedevice using the cell structure to functional state, also in connectionof a calibration of recurring nature.

In an embodiment according to the invention, the state vectorsY.sub.sto.sub.—.sub.i and/or Y.sub.sto.sub.—.sub.o have been stored tomemory so that they can be used and/or updated on the basis of themeasurement result in the measuring action performed after the actualcalibration. In another embodiment according to the invention, the statevector is iterated during the measuring action on the basis of theresults for specifying the analysis result.

As the ion 301 coming from the ionisation section passes in the driftingchamber 200 along the average route 312 of the ion 301 to the analysissection and in it within the reach of the electric field 315, it (315)deflects the travel of the ion 301 from the route 312 so that it 301 ispassed to the electrode 314 where the ion 301 will stay to convey itscharge to the electrode 314 as a second ion 311 passed there earlierthat has not yet had time to convey all of its charge to the electrode314. As the charge has been conveyed, the former ion can now leave theelectrode 314 as a neutral molecule or similar or to react with thesurface, either chemically by binding to it or, due to adhesion-typeforces, to stay in some vacancy of some structure of the surface. Onealternative for the former ion is to leave the drifting chamber 200 withand/or like the other gas particles.

In FIG. 3A, the ion 301 has been marked with a negative charge.According to a momentary situation, the route 312 of the ion in theelectric field 315 has been drawn as directing away from the electrode313 in FIG. 3A. The electric field is achieved between the electrodes313 and 314 by coupling a voltage with a suitable polarity between them.If the charge of the ion 301 were opposite in relation to the one markedin the figure and, nevertheless, the electrode 313 were in a morenegative potential than the electrode 314, the ion 301 would movetowards the electrode 313. If again the direction of the electric field315 were now changed to the direction of the arrow in the figure andback to opposite again, also the path of the ion in the analysis sectionchanges, following the change of the electric field in a manner, whichalso depends on the electric mobility of the ion 301.

The electric field 315 can consist of an electric field of a constantvalue and/or such an alternating electric field, which has a certaindirection, amplitude and frequency suitable for the appropriate purposeso that, for example, ions with a certain mobility can be picked ontothe electrode 314.

In such a case, it is also possible to arrange a certain temporalduration to the electric field, and to vary its temporal duration sothat different kinds of control conditions can be realised to beutilised in the defining of ion mobility. The voltage between theelectrodes in the reference electrode pair has to follow the voltagebetween the electrodes in the analysis electrode pair in a certain way.Most preferably the fields of the reference cell and the analysis cellhave the same phase, frequency and amplitude, as the electrodes havesimilar mechanical dimensions. The similarity must then be understood tomean similarity with a certain manufacturing-technical accuracy, and thesame phase so that delays caused by the flow of gas and/or functions ofelectronics have been taken into account in the integration.

An embodiment, according to the invention, comprises a referenceelectrode, which has been disintegrated into sub-electrodes. In thiscase, the sub-electrodes operate under a same control so that saidcontrol to each sub-electrode is dependent on, but not necessarily thesame as the control of the sub-electrodes of some other disintegratedreference electrode. Separate sub-signals can be formed from thesubelectrodes, which can be processed separately and/or summed in asuitable way in a suitable phase for providing a total signal,ultimately aimed for improving the accuracy of the mobility analysis.

An embodiment, according to the invention, contains such electrode pairsas the electrode pair consisting of the reference electrodes 303 and304, reference electrode pairs, sequentially in the flow direction ofthe sample in the reference section of the drifting chamber. In thiscase, the electrodes of the reference electrodes that operate forreceiving the ion charges, such as the electrode 304, do not have to beequally long in relation to each other in the travelling direction ofthe sample, but they can also be of different lengths and/or differentshapes, even of different widths. Advantage can then be achieved byvarying the electric conditions used for the determining of mobility.

One advantageous embodiment according to the invention contains suchelectrode pairs as the electrode pair consisting of the analysiselectrodes 313 and 314, analysis electrode pairs, sequentially in theflow direction of the sample in the analysis section of the driftingchamber. In this case, the electrodes of the analysis electrodes thatoperate for receiving the ion charges, such as the electrode 314, do nothave to be equally long in relation to each other in the travellingdirection of the sample, but they can also be of different lengthsand/or different shapes, even of different widths.

However, it can be stated that the electric properties of the referenceelectrode pair and the analysis electrode pair have to be identical witha certain accuracy for obtaining the best possible benefit of the use ofthe reference electrodes. According to the inventional idea it is,however, possible to also use non-identical reference and analysiselectrode pairs, but in this case, the differences in the their electricproperties caused by the non-identicality are of such a nature that theycan be taken into account with a certain accuracy when forming referenceand/or analysis electrode pairs. As an example of said possibledifferences between the electrode pairs, the distance between theelectrodes in the electrode pair, their shape and size, and alsomaterial, especially surface material, are given. The surface materialalso has an important role when the electric properties of differentelectrodes are evaluated in a long time interval. Namely the electrodesurfaces, for example, when they are made of metal, have a tendency toform compounds with certain components of the gas sample so that theconductivity properties can change on the electrode surfaces along withtime. In addition, in some especially disadvantageous conditions of use,the particulate substances can find their way in one form or another tosome electrode surfaces so that, when depositing to these, theparticulate-substances can also change the conductivity properties ofthe electrode surface, to which it settles.

B. Second Advantageous Embodiment

FIG. 3B discloses an example of a second advantageous embodimentaccording to the invention, as a second order cell structure 300. InFIG. 3B, there is outlined with a closing broken line the area which forthe main part substantially contains a first order cell structure 200Aaccording to FIG. 3A, which cell structure however deviates in itsgeometry from the cell structure shown in FIG. 3A with regard to thearrangement of ionisation, the ionisation section being neverthelesssubstantially between the reference section and the analysis section asin FIG. 2. It can also be stated that the cell structure 200A in FIG. 3Adiffers from the cell structure 300 in FIG. 3B with regard to thedivider plate, which is indicated with the reference numbers 344 and343, and in which the part 344 refers to the uniformly closed section ofsaid divider plate, and the part 343 to such a section of the samedivider plate, which is provided with an aperture or several apertures.The part 343 of the divider plate with apertures is most preferablyarranged at an electrode pair, the electrode pair containing a firstelectrode 303, 313, 323, 333, and a second electrode 304, 314, 314, 334.The divider plate functions as to distribute the flow in the secondorder cell structure to parts, to the one of which ionisation effect isdirected and to another one of which not. With the design of the dividerplate it is possible to influence the profile of the gas flow. Thedivider plate can be flat, but it can have a certain design in a certainpart for forming the flow profile of the gas flow; however, in the end,for optimising the mobility analysis. In this case, advantage may begained by the design, especially at the place of the input apertureand/or the input of the ionisation section, or in other places in whichthe geometry and thus the profile of the gas flow can change. Forexample, the divider plate can be provided with suitable design for theionisation section for achieving a sufficient input flow. It can furtherbe stated that it is possible to use the different designs of thedivider plate to influence the mixing of gas, either in a balancing orpromoting manner. The design of the divider plate can also be used forinfluencing the flow quality in the vicinity of the formed section ofthe divider plate, whether it is turbulent, laminar, or in a transitionregime there between.

The closed part 344 of the divider plate is most preferably arranged atthe ionisation section to prevent ionisation effect on the part of thesample gas that passes through the drifting chamber 200 along its part342 past the ionisation section. If the radiation field 306 is used forachieving ionisation, the material and/or material strength of thedivider plate shall then be most advantageously selected according tothe components of the radiation field 306 so that the ionisation effectis minimised in the part 344 of the divider plate facing the driftingchamber 200 and is thus restricted to the part 341 to its certainvolume.

So that the structural unit 210 of gas moving with the gas sample flow100 entering the cell structure through the inlet 204 could change tothe ion 301 in due course, when arriving to the ionisation sectionrestricted by the broken lines 220 and 221, it 210 has to move on thatside of the part 344 of the divider plate in the drifting chamber 200which is indicated by the reference number 231, at least at theionisator. The part 344 of the divider plate can have the electrode 308integrated into its structure, or the plate part 344 itself can act asthe electrode for generating the electric field. Ionisation can be basedon corona discharge. In this case, for maintaining the corona dischargewith the help of an electric field, the ionisation section has mostpreferably at least two electrodes 307 and 308, the corona dischargeoccurring between said electrodes due to the electric field between themas the strength of said electric field is generated by the sufficientpotential difference between the electrodes 307 and 308.

In the cell structure in FIG. 3B, the drifting chamber 200 is limited bythe planar part 322 and the plane 302. The part 302 can be formed inaccordance with the figure, in which case it can have apertures formaking possible a certain design of the flow channel. The support 318 isconnected to the planar part 322 drawn in the figure for supporting thedivider plate including the parts 323 and 344. For separating saiddivider plate from the part 302 belonging to the cell structure in thecell structure in FIG. 3B, it has a support part 317. The parts can mostpreferably be shaped for providing a gas flow channel for the input 204and output 205 of the gas flow 100 so that also the wall part 354 of thechannel can be used for the shaping. For fastening the electrodes inFIG. 3B, such insulating materials can be used in the selection ofmaterials, that the resistivity, especially surface resistivity of whichis stable and most preferably, as high as possible for eliminatingleakage currents in the electric operating range of the electrodes.

The divider plate with the parts 343 and 344 can be made, for example,of stainless steel, capton, or PTFE. One possible insulating materialcan be stainless steel coated with a titanium nitride coating. It isespecially suitable for space-technical applications, as it is inert andelectrically stable. The use of the electric field in the ionisationsection 202 can require that the electrode 308 be insulated from thedivider plate. Upon using insulating material in the divider plate, theelectrode 308 can be attached directly to it. FIG. 3B shows an electrodepair, a front field electrode pair, comprising the electrodes 323 and324 for forming a specific front field. The electrodes in the area ofthe front field electrode pair belong to the front cell. The function ofthe front field of the front cell is to remove charge-carrying particlesand/or ions from the gas sample that are inappropriate for the mobilityanalysis of ions so that they would not get deeper in the flow ofdirection to hinder the charging and thus also the forming of themobility spectrum. In addition, the counter-electrode 324 of the frontfield can be utilised as a measuring electrode, and the signal obtainedfrom it directly or the information to be formed on the basis of it canbe used in the actual gas measurement and in the identification of ions.

FIG. 3B also shows a second electrode pair, a back field electrode pair,consisting of the electrode 333 and electrode 334, which belong to theback cell. The purpose of the back field electrode pair of the back cellis to provide an electric field, the back field, after the analysiselectrode and behind it, and to make possible the realtime measurementof gas rate with the help of it. Because the collection efficiency ofthe analysis electrode pair depends on the voltage between itselectrodes, it is possible that part of the ions will not be aggregatedonto the analysis electrode pair. When voltage is coupled between theelectrodes in the back field electrode pair, the ions that have not beenaggregated to the analysis electrode can be collected with the help ofthe back field electrodes. The electric field generated by the actualanalysis electrode pair can vary, for example, sinusoidally. In thiscase, the field strength and/or frequency of the back field can mostpreferably be bound to the respective quantities of the analysis voltageand, most preferably, the reference signal can also be utilised forforming the signal obtained from the back field, the back field signal.The aggregation of ions onto the back field electrode generates chargechanges in it so that a back field signal can be formed from the backfield electrode 344 analogically in a similar way as an analysis signalis formed from the analysis electrode 314. The shape of the back fieldsignal can differ from the analysis signal, for example, due todistortion and/or phase shift. On the basis of the phase shift, it isthen possible to determine the gas rate by comparing certain waveformsof the analysis signal and the back field signal with each other. Inthis case, the waveform of an analysis signal occurring in a certaintime interval has a certain delay, which depends on the gas flow rate,before the respective waveform can be observed from the back fieldelectrode in the back cell a certain time later. For example, a delaydetermination based on autocorrelation function can then be used. Inthis case, the flow rate of the gas flow 100 can be measured real-timetogether with the ion measurement. In addition, the back field signalcan be processed, for example, with a measuring amplifier, which,however, has not been drawn to the FIG. 3B. Neither does the figure showother amplifiers (amplifiers or similar needed for amplifying and/orprocessing the analysis signal and reference signal) and/or voltagesources, nor means needed for controlling these, nor other means used,for example, for filtering the signals.

In the cell structure according to an embodiment of the invention, thegeometry and size of the back field electrode pair are most preferablyselected on the basis of the collection efficiency of the analysiselectrode pair and the phase difference, and the allowable measurementerror in it.

In the cell structure according to an advantageous embodiment of theinvention, a back field electrode is a part of the disintegratedanalysis electrode so that also the back field can be utilised in theidentification.

In the measurement of gas rate performed with the help of the back fieldelectrode pair, advantage is gained in relation to techniques based onpressure difference and mass flow measurements, for example, in that themethod utilising the back field electrode is not dependent on thedensity and thus humidity of the sample gas and/or the concentration ofthe sample gas as in the methods based on mass flow and pressuredifference measurements.

In the next example, the operation of the cell according to FIG. 3B isexamined. The sample gas is taken along the drifting chamber 200 withinthe reach of the reference electrode pair and thus to the electric fieldbetween the electrodes in said electrode pair. The gas flows furtherpast the ionisation section (the section of the drifting chamber 200 inpart 341 limited between the extensions of the broken lines 220 and 221)so that the gas is ionised in a certain way which is determined by theproperties of the ionisation source, charger. As the gas flow advancesto the place of the analysis electrode pair to the electric fieldbetween the electrodes in the electrode pair, the generated ions can beanalysed with the help of the electric field formed by the analysiselectrode pair.

With a divider plate provided with the parts 343 and 344, it is possibleto realise the cell structure of an advantageous embodiment according tothe invention in accordance with the second order cell structure, butwith a simple mechanical structure. In this case, the gas flow passingon the side of the divider plate 341 facing the charging part of theionisation section is charged, as again the part of the gas flow passingon the other side 342 of the divider plate, is not charged. The portionof the volume flow of the charged gas relative to the volume flow of theuncharged gas can then be optimised to be most advantageous for themeasurement accuracy by placing the divider plate to a suitable distancebetween the plates 302 and 322, substantially in their direction. Inthis case, the parts 317 and 318 of FIG. 3B can be arranged tocorrespond to different measurement geometries with a different ratio ofthe volume of charged gas to the volume of uncharged gas. It is thenalso possible to make the dimensions of the chamber 200A arrangeable andthus adjustable. The parts 317 and 318 can then also consist of severalparts, these parts forming a certain tuning set for optimising thedimensions of the cell structure for a certain gas measurement. With thedivider plate it is also possible to minimise flow mechanicalinterferences in the gas flow.

In according to an advantageous embodiment of the invention, the dividerplate with the parts 343 and 344 can be provided with means for couplingvoltage between the divider plate and a part in reference potential—forexample ground potential—analogically, as to a gate of a radio tube ofthe triode type, in which case the voltage to be coupled to the dividerplate can be used for controlling the moving of ions through theapertures of the divider plate to one analysis electrode in a similarway as the gate voltage of a radio tube is used for controlling the flowof electrons between anode and cathode.

C. A Number of Other Advantageous Embodiments

FIG. 4A presents a diagram, in which a device 400, a gas measuringdevice 400, according to an embodiment of the invention is shown as anexample. This has the cell structure 200A that is shown in FIG. 3A. Thegas measuring device 400 can also have the cell structure 300 accordingto FIG. 3B. Such a gas measuring device vice is illustrated in FIG. 4B.The gas measuring device 400 can also have a number of cell structures,in which each cell structure is then optimised for detecting themobility of ions within a certain mobility range between a certainminimum mobility and a maximum mobility. By using several cellstructures parallel, it is then possible to cover a wider mobility rangethan by using a single cell structure. The price to be paid is then thatthe number of control and other devices needed is increased and/or thecontrol becomes more complicated. In this case, the device can also havecell structures of either type or both types, for optimising themobility range. For example, one of the cell structures to be used inparallel can be arranged to identify positive ions and a second one toidentify negative ions. It can also be stated that by using several cellstructures in parallel in the measuring device, the redundancy of themeasuring device can be increased, which is useful against failuresituations. In addition, with the device of several cell structures itis possible to perform measurements, in which it is necessary to phasethe mobility analysis of ions for identifying certain substanceswithout, for example, having to rinse the chamber between analyses,which would be necessary, for example, with a device provided with asingle cell structure in a respective situation. It is also possible tomeasure both positive and negative ions simultaneously fromsubstantially the same environment.

The markings drawn to FIG. 4A in a gas measuring device 400 according toan advantageous embodiment of the invention have the first order cellstructure 200A according to FIG. 3A, formed by an aspiration condenser.In this case, the markings in FIG. 4A in the cell structure have thereference cell 411, the ionisation section 410, and the analysis cell409, in said order in the direction of advance of the gas sample alongthe analysis chamber.

As an example of an advantageous embodiment of the invention, with themarkings drawn in FIG. 4B, the device 400, has a second order cellstructure 300 according to FIG. 3B, formed by an aspiration condenser;the cell structure thus also having a divider plate. In this case,according to the markings of FIG. 4B there are reference cell 411, theionisation section 410 and the analysis cell 409, in said order in thedirection of advance of the gas sample along the analysis chamber.However, the cell structure of the device 400 in FIG. 4B then has afront cell 414 before the reference cell. The front cell is then mostpreferably realised with the help of a front field electrode pairconsisting of the electrode 323 and the electrode 324, as is shown inconnection of the cell structure 300 in FIG. 3B. In the example in FIG.4B, still the back cell 415 has been shown of the cell structure, placedafter the analysis cell 409 in the flow direction of the sample gas. Theback cell is then most preferably realised with the help of a back fieldelectrode pair comprising the electrode 333 and the electrode 334, as isshown in connection of the cell structure 300 in FIG. 3B. With the helpof the back field electrode, it is possible to determine the averagerate of the gas flow 100.

The front cell and/or back cell can also be eliminated from such asecond order cell structure, which is illustrated in FIG. 3B. In such acase, the advantages offered by the cell-left-out from the cellstructure and thus from the device are not achieved, but tocounterbalance this, the cell structure in itself is simpler so that, onthe other hand, space can be saved from the device 400.

The gas measuring device 400, according to an advantageous embodiment ofthe invention, has the microprocessor 406 for maintaining andcontrolling its 400 analysis and other functions and for processing thesignals obtained from the reference and analysis electrodes. Inaddition, the device 400 can have specific means for processing thesignal obtainable with the help of an electrode in the front and/or backfield electrode pair in the cell structure 300, the means mostpreferably being programmatic.

In FIGS. 4A and 4B, there is shown the amplifier 412 for amplifying thesignal coming from the reference cell 411; in the examples in Figures,the amplifier can be controlled by the microprocessor 406. In thefigures, the amplifier 422 has also been drawn connected to the analysiscell 409. However, an amplifier can also be connected to the front cell414 and/or back cell 415 drawn in FIG. 4B for amplifying a signal and/orfor processing the available signals, although such are not shown inFIG. 4B. In this case, the amplifier in question can most preferably becontrolled by the microprocessor 406, at least in part.

The amplifiers 412 and 422 have been drawn connected to the comparatormeans 407, which is also in contact with the microprocessor 406. Thecomparator means 407 can have several inputs, for example, one for eachsignal obtainable from the electrode of a cell. The comparator means 407can also comprise signal processing means for processing an incomingsignal, which most preferably have been arranged ultimately foroptimising the identification of ions. The comparator means 407 is incontact with the microprocessor 406 for feeding the analysis signalcoming through the comparator means to the microprocessor for actions tobe performed with it.

In FIGS. 4A and 4B there is a drawn amplifier 412 connected to thecomparator means 407, and by a bi-directional connection to themicroprocessor 406 so that a reference signal can be directly obtainedfrom the amplifier 412 to the microprocessor 406 suitably amplified andformed to digital form, as its 412 one output has the necessary analogueto digital converter. The reference signal can be obtained to themicroprocessor 406 also through the comparator means 407. Respectively,also a signal originating from the electrode of some other cell 409,410, 414, 415 can be amplified and routed, when necessary, directly tothe microprocessor 406 in digital form, or the signal can be routedthrough the comparator means 407, for example, for connecting the signalto other signals or parts of these in a particular way.

From each amplifier, with which a signal to be obtained from a cell 409,410, 411, 414, 415 is amplified, but of which only the amplifiers 412and 422 have been drawn in the FIGS. 4A and 4B, there can be provided aconnection to a separate input in the comparator means 407. For example,the comparator means 407 can have an analogue input and a digitaloutput. In this case, a microprocessor 406 can be used to control thefunctions of the comparator means 407 for processing the signal, whichcan be performed also programmatically in the microprocessor, whenapplicable, for saving space and/or components.

The microprocessor 406 and some software means operating in it can thenbe used for analysing the analysis signal, for processing it, forexample, by filtering and to form the mobility spectrum of ions. On thebasis of the mobility spectrum, the type of ions incorporating into themobility spectrum can be identified. Most preferably, the microprocessor406 also has a connection to some memory means for saving necessaryprograms, control parameters and/or other data used in theidentification, although the examples in FIGS. 4A and 4B do notseparately show the memory in the device 400. Most preferably, theidentification of ions is based on librarised data, which can form adatabase, which can be, for example, a relational database.

In the device 400, according to an advantageous embodiment of theinvention, there are further provided the transmitter-receiver means 404for controlling the analysis operation and preferably also an antenna403 or similar for maintaining the functional control connection betweenthe device 400 and the device 401 controlling it and/or the operator. Inthis case, the microprocessor 406 is most preferably connected also tothe transmitter-receiver means 404 so that data transmission justbetween these is possible.

In FIGS. 4A and 4B, a mobile station has been drawn as the controllingdevice 401, but it can also be some other radio device, for example, aradio telescope in space-technical applications, or an infraredtransmitter. In this case, the message 402 intended to travel betweenthe gas measuring device 400 and its controlling device 401 can comprisean impulse for controlling the gas measuring device 400 or, as aresponse to an impulse, a report on the measuring results and/or thestatus of the gas measuring device 400 to be received, for example, withthe device 401. An impulse can then be used for commanding the device400 to set certain values for the quantities influencing the analysisoperation as a response to said impulse. Such quantities, as the voltagebetween the electrodes in the electrode pair of a certain cell, itswaveform and/or frequency can be given as an example.

In FIG. 4A it has been shown that the microprocessor 406 is in contactwith the control means in the voltage sources 405 and/or 413, and inFIG. 4B, in the voltage sources 423 and/or 425. In this case, a controlmeans, which most preferably is in the voltage source 405, 413, 423, 425as its part, can be arranged for controlling one or several parts of thecell structure; for example, the reference cell 411, the ionisationsection 410, the analysis cell 409, the front cell 414 and/or the backcell 415 according to the controls of the microprocessor 406. Thevoltage sources 405, 413, 423, 425 used in the cells and/or theionisation section for forming the necessary voltages most preferablycomprise said control means. Each control means has the necessary numberof inputs for controlling the output voltages of a certain voltagesource. The polarity of the output voltage of a certain voltage source,its nominal voltage, amplitude, waveform and/or frequency are mostpreferably controllable in an independent way according to the need ofthe cell in each cell structure for making possible the reliability of acertain level for the identification of ions.

In FIG. 4B, the voltage source 423 is drawn to have a different numberof outputs implemented for the feeding of parts of the cell structurefrom the voltage source 413 in FIG. 4A. In FIG. 4B, the voltage source425 is drawn to have a different number of outputs from the voltagesource in FIG. 4A implemented for the feeding of parts of the cellstructure. Because of this, the reference numbers for the voltagesources are different between FIGS. 4A and 4B, although the voltagesources as such would have no other difference.

The gas measuring device 400 can also be set to report data concerningits own status and/or send analysis results, and to use a certain formof communications for sending these. The device can be a device intendedto be fixedly installed in a laboratory, a device suitable forcross-country and/or a portable device intended to be used on Earth forthe identification of certain gaseous substances. The device can also bearranged for the identification of gases in mine conditions, tunnels, aspace ship, a submarine, or some other space, for example, in alaboratory or fume hood, in which the composition of the gases hassignificance.

FIG. 5 illustrates a method according to an advantageous embodiment ofthe invention for identifying the electric mobility of ions of thecarrier gas with the help of electric fields. In this case, a firstelectric field is formed between a first reference electrode and asecond reference electrode (500A), and a second electric field is formedbetween a first analysis electrode and a second analysis electrode(500B).

After the electric fields have been formed, a gas sample is taken (501)in the method, which gas sample is processed (502), for example, toremove particles, but also heavy or light ions can be removed from it,which as such can have a detrimental influence on the analysis accuracyand/or the cell structure as such. The particles to be removed can besolid and/or liquid material. The forming of electric fields can also beinterpreted so that an electric field is changed from a first state to asecond state different than said first state. In addition, mostpreferably as a continuous method, it can have several phases inprogress at least in part simultaneously.

In the method, the sample gas is first directed through the referencecell for producing a reference signal, the sample gas is charged to beelectrically charged in said ionisation section for providing a certainelectric charge to a certain relative part of the number of structuralunits of the sample gas, and as the sample gas flows further to theanalysis cell after the ionisation section, the ions in the sample gasare analysed, based on their electric mobility.

The sample gas is analysed (503) for producing a first signal, on theone hand, on a reference electrode and, on the other hand, for forming asecond signal on an analysis electrode, on the basis of changes ofcharge in the reference electrode and analysis electrode. Also chargingthe sample gas in the ionisation section relates to the analysis, theionisation section being located between the reference section and theanalysis section. The mentioned first and second signals are processed(504) for generating a processed signal, on the basis of which amobility spectrum is provided, which is used in the identification (505)of the ion. For example, a suitable deconvolution algorithm can be usedin the identification. The identification can also be based onlibrarised data or a similar database of the mobility spectrum. Inaddition, the mobility spectrum to be formed on the basis of theprocessed signal can be reported forward either before or after theidentification, on the basis of a functional data transmissionconnection, for example by way of a radio. It is also possible to sendmerely the processed signal for performing the identification itself ina disintegrated manner, for example, outside the means or a similardevice processing the signal. The disintegrated analysis can beadvantageous, for example, in a space-technical application or in such acase in which the cell structure itself is either far away and/or in aclosed space for analysing hazardous substances.

In a method according to an advantageous embodiment of the invention,the particle-shaped solid and/or liquid material can be removed byvaporisation. In this case, the temperature of the cell structure has tobe kept constant so that all the material arriving at the analysis cellof the cell structure is most preferably in gas phase. For reducing thechanges caused by particles on electrode surfaces, for example, at leastthe analysis cell can be rinsed with a particle-free neutral gas, forexample, in a cyclic measurement in which sample gas is measured forpart of the time and rinsed for part of the time.

As an example of the preferable dimensions of the cell structureaccording to an embodiment of the invention it can be stated that theheight of the drifting chamber of the cell structure, referring to thedistance between the electrodes in the electrode pair (for example, 313and 314) is about 0.1-10 mm for a drifting chamber with first or secondorder cell structure according to an advantageous embodiment of theinvention. With the chamber of second order, the distribution plate ismost preferably within a distance of 0.05-9.95 mm from an analysiselectrode. In the cell structure according to an advantageous embodimentof the invention, the gas flow rate is approx. 0.1-10 l/min. Thedetailed selection of the flow rate depends on the ion flux, thegeometrical dimensions of the cell structure and/or device in general,and the pump required for maintaining the flow. Table 1 shows examplesof the use parameters for some advantageous embodiments according to theinvention. The Table do not mention a free waveform, which can bepresented with the help of an exponential function based signals bycombining them. TABLE-U.S. Pat. No. 00001 TABLE 1 Examples of the useparameters of some advantageous embodiments according to the inventionfor first and/or second order cell structures Cell The electric field ofthe cell structure Frequency Amplitude Direct voltage type (Hz) Waveform(|V|) component (|V″) Front cell 0 or 1-1000 DC or sine, tri-12 12 or 0(when the angle, ramp signal is not DC) Reference 1-1000 Sine, triangle,120 cell ramp Analysis 1-100 Sine, triangle, 120 cell ramp Back cell 0or 1-1000 DC or sine, tri-12 12 or 0 (when the angle, ramp signal is notDC)

1. A method for an identification of substances in a flowing gas, basedon electrical mobility of ions comprising: (a) setting a first electricfield between electrodes in a reference electrode pair; (b) setting asecond electric field between electrodes in an analysis electrode pair;(c) transporting a gas sample through the reference electrode pair, anionization section and the analysis electrode pair in said order; (d)analyzing the gas sample; (e) forming a mobility spectrum of ions; and(f) identifying an ion from the gas sample on the basis of the mobilityspectrum.
 2. A method according to claim 1, wherein changes in charge onthe electrodes in the reference electrode pair are observed to therebyform a reference signal, said gas sample is charged for generating ions,and the changes in charge on the electrodes in the analysis electrodepair are observed to thereby form an analysis signal.
 3. A methodaccording to claim 1, wherein the mobility spectrum is formed on thebasis of a reference signal and an analysis signal generated by saidfirst and second electric fields, respectively.
 4. A method according toclaim 1, further comprising pre-processing the gas sample to therebyremove particulate solids or liquid materials before the sample arrivesat the reference electrode pair.
 5. A method according to claim 1,wherein identifying said ion a mobility library or a respectivedatabase.
 6. A method for electrically determining gas flow velocity inan aspiration condenser, comprisings condenser, (a1) setting a firstelectric field between electrodes in a first electrode pair comprising afirst electrode; (a2) setting a second electric field between electrodesin a second electrode pair, comprising a second electrode; (a3) settinga third electric field between electrodes in a third electrode paircomprising a third electrode; (a4) observing changes of charge of thefirst, second and third electrode in said first, second and thirdelectric field; (a5) correcting changes of charge detected, using saidsecond electrode and said third electrode, on the basis of the changesof charge detected on the first electrode; (a6) determining the time,passing between the occurrence of changes of charge on the secondelectrode and on the third electrode; and (a7) calculating the gasvelocity, wherein said aspiration condenser comprises a cell structurehaving a flow channel for controlling the gas flow, a reference cellarranged to form a reference signal, an ionization section for achievingan ionization effect into the sample gas, and an analysis cell arrangedto form an analysis signal so that the reference cell, the ionizationsection, and the analysis cell are located in said order in thedirection of flow of the
 7. A method according to claim 6, wherein anautocorrelation function is formed for determining the time between thedetected changes of charge on the second and third electrode.
 8. Amethod for identification of substances in a flowing gas sample as basedon a cell structure and ion mobility of the ions, comprising:controlling the gas flow by a flow channel in the cell structure;forming a reference signal; achieving an ionization effect into the gassample; forming an analysis signal, wherein said forming the referencesignal, achieving the ionization effect and forming the analysis signalare implemented by a reference cell, an ionization section and ananalysis cell, respectively said reference cell, said ionizationsection, and said analysis cell, being arranged into said order in theflow channel.
 9. The method of claim 8, wherein a first electric fieldis set between electrodes in a reference electrode pair, a secondelectric field is set between electrodes in an analysis electrode pair,the gas sample is taken to be transported through the referenceelectrode pair, the ionization section, and the analysis electrode pairin said order, the gas sample is analyzed, a mobility spectrum of ionsis formed, and an ion is identified from the gas sample on the basis ofthe mobility spectrum.
 10. The method of claim 9, wherein, in analyzingthe gas sample, changes of charge on the electrodes in the referenceelectrode pair are observed to thereby form a reference signal, the gassample is charged to generate said ions, and changes of charge on theelectrodes in the analysis electrode pair are observed to thereby ananalysis signal.
 11. The method of claim 9, in which said mobilityspectrum is formed on the basis of the reference signal and the analysissignal.
 12. The method of claim 9, further comprising pre-processing thegas sample to remove solid or liquid material before the gas samplearrives at the reference electrode pair.
 13. The method of claim 9, inwhich identifying said ion from said gas sample is based on a mobilitylibrary or a respective database.